This invention relates to nitrogen atom-containing polysiloxanes which can be synthesized from inexpensive reactants and useful as the main component of fiber and fabric finishing agent compositions for imparting softness and durability of home laundering to a variety of fibers or fibrous materials, methods for preparing the same, and fiber and fabric finishing agent compositions.
A number of organopolysiloxanes such as dimethylpolysiloxanes, epoxy group-containing polysiloxanes, and nitrogen atom-containing polysiloxanes have been widely used as treating agents for imparting softness and smoothness to a variety of fibers or fibrous materials. Most widely used among others are the nitrogen atom-containing polysiloxanes, especially aminoalkyl group-containing organopolysiloxanes, which can impart satisfactory softness to a variety of fibers or fibrous materials. More specifically, fiber treating agents based on organopolysiloxanes having such aminoalkyl groups as xe2x80x94C3H6NH2 and xe2x80x94C3H6NHC2H4NH2 are widely used because of their softness capability as disclosed in JP-B 48-1480, JP-B 54-43614, JP-B 57-43673, JP-A 60-185879, JP-A 60-185880, and JP-A 64-61576.
These nitrogen atom-containing polysiloxanes are generally synthesized by equilibrating with alkalis dimethyl cyclics such as 1,1,3,3,5,5,7,7-octamethyl-cyclotetrasiloxane, nitrogen atom-containing trialkoxy-silanes, nitrogen atom-containing cyclopolysiloxanes, etc.
In the silicone industry, the dimethylsiloxy sources for polysiloxanes are dimethyl cyclics obtained by hydrolyzing dimethyldichlorosilane and distilling the hydrolyzate, and xcex1,xcfx89-dihydroxydimethylpolysiloxane which is the still residue. Since the former is in greater demand than the latter, the latter is converted by cracking into the former as needed. As compared with the former, the latter is inexpensive.
Since the nitrogen atom-containing polysiloxanes as typified by aminoalkyl group-containing organopolysiloxanes are currently used for general purposes, there is an increasing demand for cost reduction. If xcex1,xcfx89-dihydroxydimethylpolysiloxane could be used as the starting reactant, it would become possible to synthesize nitrogen atom-containing polysiloxanes in an inexpensive manner. There is a need for such a synthetic method.
As the method for obtaining higher molecular weight polysiloxanes from xcex1,xcfx89-dihydroxydimethylpolysiloxane as the starting reactant, alcohol-removing reaction with alkoxysilanes is known. However, a high temperature or a catalyst is essential for this reaction because of low reactivity. British Patent No. 9,188,239 discloses the use of an amino compound salt with phosphoric acid or carboxylic acid as the catalyst. Japanese Patent No. 2,857,203 discloses the use of strontium hydroxide or barium hydroxide as the catalyst. However, the amino compound salts with phosphoric acid or carboxylic acid give rise to a yellowing problem when applied to white or tint color fibers or fibrous materials. Additionally, it is difficult to remove the catalyst from the product since most of these catalysts are liquid. On the other hand, such catalysts as strontium hydroxide and barium hydroxide also become foreign matters in the fiber treating step and cause cracking of polysiloxanes. This necessitates an extra step of removing the catalyst. An efficient reaction method without a need for a catalyst is thus demanded.
Among prior art nitrogen atom-containing poly-siloxanes, aminoalkyl group-containing organopolysiloxanes are most common. They suffer from the problem that the softness imparted thereby lowers during long-term use or by repeated washing. There is a need for nitrogen atom-containing polysiloxanes having long-lasting performance.
JP-B 46-3627 discloses the condensates of xcex1,xcfx89-dihydroxydimethylpolysiloxane with amino group-containing alkoxysilanes, but reaction conditions are described nowhere. In Examples described therein, the ratio of the moles of xcex1,xcfx89-dihydroxydimethylpolysiloxane to the moles of amino group-containing alkoxysilane is 0.07 or 0.02. These ratios are outside the range used in the present invention. Also, JP-A 6-184257 discloses analogous condensates, but no reference is made to the preparation method. No alkoxy groups are left in these condensates, that is, all alkoxy groups are replaced by xcex1,xcfx89-dihydroxydimethylpolysiloxane. This structure differs from the polysiloxanes of the present invention. Further, U.S. Pat. No. 3,355,424 discloses piperidyl group-containing organopolysiloxanes which are prepared by hydrolytic condensation of an addition product of allyloxypiperidine and a dialkoxysilane. This preparation method differs from the method of the present invention. No alkoxy groups are left in these condensates.
Further, fibers treated with organopolysiloxanes having such aminoalkyl groups as xe2x80x94C3H6NH2 and xe2x80x94C3H6NHC2H4NH2 suffer from degradation of amino groups by heat or ultraviolet radiation during heat treatment, drying or aging. In particular, white or tint color fibers or fibrous materials treated with such organopolysiloxanes have the serious problem that their color changes to yellow and their softness lowers during heat treatment, drying or aging.
For preventing the yellowing problem, it was proposed to modify aminoalkyl group-containing organopolysiloxanes, for example, by reacting the aminoalkyl groups with organic acid anhydrides or chlorides (JP-A 57-101046), epoxy compounds (JP-A 59-179884), higher fatty acids (JP-A 1-306683), and carbonates (JP-A 2-47371).
As compared with the unmodified aminoalkyl group-containing organopolysiloxanes, these modified organopoly-siloxanes were found to be improved in anti-yellowing effect, but to a still insufficient extent. With respect to the impartment of softness and smoothness to fibers or fabrics, the modified ones are rather inferior to the unmodified ones.
An object of the invention is to provide a novel and improved nitrogen atom-containing polysiloxane which is effective as a main component of a fiber-treating agent composition for imparting softness and smoothness to fibers or fibrous materials while minimizing the yellowing thereof.
Another object of the invention is to provide a novel and improved nitrogen atom-containing polysiloxane which is effective as a main component of a fiber and fabric finishing agent composition for imparting to fibers or fibrous materials a softness which is not only high at the initial, but also lasts even after washing.
A further object of the invention is to provide a method for preparing the nitrogen atom-containing polysiloxane.
A still further object of the invention is to provide a fiber and fabric finishing agent composition comprising the nitrogen atom-containing polysiloxane as a main component.
We have found that an organopolysiloxane having some alkoxy groups left intact is effective for enhancing the bond to a substrate and improving softness, and durability of home laundering. In the resulting polymer, amino group-containing silicon atoms are not present as blocks, but regularly distributed in accordance with the degree of polymerization of xcex1,xcfx89-dihydroxypolysiloxane. This feature is the largest difference from the polymers prepared by the prior art technique of alkali equilibration. The regular distribution of amino groups in the polymer is effective for improving softness and durability. The invention is predicated on this finding.
In a first aspect, the invention provides a nitrogen atom-containing polysiloxane having at least one polymer terminus represented by the general formula (1). 
Herein R1 is a nitrogen-free, substituted or unsubstituted, monovalent organic group of 1 to 20 carbon atoms, R2 is a monovalent organic group containing at least one nitrogen atom, R3 is an organoxy group represented by xe2x80x94OR1, and p is a positive number of 2 to 2,000.
In a second aspect, the invention provides a method for preparing a nitrogen atom-containing polysiloxane as defined above, comprising the step of effecting alcohol-removing reaction between (A) an organopolysiloxane of the general formula (5): 
wherein R1 and p are as defined above and (B) an organosilane of the general formula (6): 
wherein R1, R2, and R3 are as defined above.
In a third aspect, the invention provides a nitrogen atom-containing polysiloxane comprising at least one unit represented by the general formula (11). 
Herein R1 is a nitrogen-free, substituted or unsubstituted, monovalent organic group of 1 to 20 carbon atoms, R2 is independently a monovalent organic group containing at least one nitrogen atom, R3 is an organoxy group represented by xe2x80x94OR1, and p is a positive number of 2 to 2,000.
In a fourth aspect, the invention provides a method for preparing a nitrogen atom-containing polysiloxane as defined above, comprising the step of effecting alcohol-removing reaction between (A) an organopolysiloxane of the general formula (5): 
wherein R1 and p are as defined above and (C) an organosilane of the general formula (13): 
wherein R2 and R3 are as defined above.
Also contemplated herein is a fiber and fabric finishing agent composition comprising the above-defined nitrogen atom-containing polysiloxane as a main component.
We have found that a nitrogen atom-containing polysiloxane in which a nitrogen atom-containing group of formula (1) is selectively introduced into the polymer terminal group, upon treatment of fibers or fibrous materials therewith, ensures efficient reaction with fiber surfaces, improves durability, minimizes yellowing by heat or UV radiation after treatment because of a reduced number of nitrogen atoms not adsorbed on fiber surfaces, prevents the fibers or fibrous materials from yellowing, and imparts excellent softness.
Although the prior art method of synthesizing nitrogen atom-containing polysiloxanes by equilibrating with alkalis dimethyl cyclics such as 1,1,3,3,5,5,7,7-octamethyl-cyclotetrasiloxane, nitrogen atom-containing trialkoxy-silanes, nitrogen atom-containing cyclopolysiloxanes, etc. is impossible to selectively introduce a nitrogen atom-containing group into the polymer terminus, the compound of the invention can be prepared by reacting xcex1xcfx89-dihydroxydimethylpolysiloxane with a nitrogen atom-containing dialkoxysilane while removing the resultant alcohol from the reaction system. Since the nitrogen atom-containing trialkoxysilane functions as a catalyst for removing the alcohol, this reaction readily takes place without a need for a catalyst.
JP-A 9-137061 discloses a nitrogen atom-containing polysiloxane prepared by alcohol-removing reaction of xcex1xcfx89-dihydroxydimethylpolysiloxane as the starting reactant. This method has the drawback that reaction is very slow in the absence of a catalyst such as sodium phosphate or barium hydroxide. Where the catalyst is used, an extra step of neutralizing or removing the catalyst is necessary, complicating the overall process. The average structure of the thus prepared polysiloxane is described in this patent although the general structure is described nowhere. It is not attempted to produce a nitrogen atom-containing polysiloxane having a nitrogen atom-containing group selectively introduced at the polymer terminus as in the present invention.
By 29Si-NMR analysis, we have found the following fact. When xcex1xcfx89-dihydroxydimethylpolysiloxane is reacted with a nitrogen atom-containing dialkoxysilane, the nitrogen atom-containing dialkoxysilane becomes a self catalyst so that the first alkoxy group may undergo quick alcohol-removing reaction without a need for catalyst, but the second alkoxy group undergoes little alcohol-removing reaction. Further, where a nitrogen atom-containing trialkoxysilane is used, this nitrogen atom-containing alkoxysilane similarly becomes a self catalyst so that the first and second alkoxy groups may undergo quick alcohol-removing reaction without a need for catalyst, but the third alkoxy group is quite poorly reactive as compared with the first and second ones.
We have thus found that by reacting inexpensive xcex1xcfx89-dihydroxydimethylsiloxane with a nitrogen atom-containing triorganoxysilane on the basis of the above-described reaction scheme, a novel nitrogen atom-containing polysiloxane having a desired degree of polymerization is readily obtainable without a need for catalyst. In the resulting nitrogen atom-containing polysiloxane, nitrogen atom-containing groups are not present as blocks, but introduced at regular intervals in the polymer, and organoxy groups are contained on polymer side chains. For this reason, as compared with prior art nitrogen atom-containing polysiloxanes, the nitrogen atom-containing polysiloxane of the invention firmly bonds with fibers, accomplishing excellent softness, long-term softness retention, and durability of home laundering.
Also, the nitrogen atom-containing polysiloxane comprising units of formula (11) is prepared by starting with xcex1xcfx89-dihydroxydimethylpolysiloxane which is the still residue after removal of cyclic polysiloxanes in the step of vacuum distilling hydrolyzates of dimethyldichlorosilane. Because low molecular weight components have almost been removed, the nitrogen atom-containing polysiloxane has a minimized content of low molecular weight components as compared with the prior art nitrogen atom-containing polysiloxanes resulting from equilibration. This minimizes the build-up problem or the contamination in a treatment dryer line by low molecular weight siloxanes.
Furthermore, the synthetic method of the invention can readily produce a silanol-terminated nitrogen atom-containing polysiloxane having a degree of polymerization of less than 200, although the prior art technique of equilibration with alkali compounds was difficult to produce such a polysiloxane.